Butterfly valves are known in the art and typically comprise a circular disk that is rotatable from a first closed position where the disk extends across a circular opening in the butterfly valve to block flow of materials therethrough to a second open position where the circular disk extends edgewise across the circular opening to permit flow of materials through the circular opening in the butterfly valve.
Examples of butterfly valves include U.S. Pat. No. 5,295,659, which shows a butterfly valve having shaft seals to prevent leakage therepast as the circular disk is rotated from an open position to a closed position or vice versa.
Another butterfly valve is shown in U.S. Pat. No. 4,836,499, which includes a two-way dynamic annular inflatable disk seal that deflates to permit opening the valve and inflates to seal around the edges of the disk to prevent leakage therepast when the valve is in a closed condition.
A butterfly valve for handling hot materials is shown in U.S. Pat. No. 8,256,448. The valve includes an annular inflatable elastomer seal that seals around the edges of the disk to prevent leakage therepast. The seal is coupled with a housing that protects the seal from contact with hot materials that may exceed a temperature that could cause breakdown or rupture of the elastomer seal.
Still other butterfly valves, which may be used to handle bulk materials that are corrosive or abrasive, contain relative massive metal disks made from noncorrosive materials. Typically, the butterfly valves with metal disks enable one to move the disk from a no flow condition to a flow condition under a variety of temperature and pressure conditions by pivoting the disk about a diametrical shaft, which supports the metal disk.